Sub-Audio Magnetics (SAM) is a "high definition" technique which measures both magnetic and electrical properties of the earth from a single survey.
SAM has two main modes of operation - Galvanic and Electromagnetic. Both modes employ a geophysical transmitter to produce an energising field.
SAM Galvanic surveys are similar to the MMR technique where current is transmitted through a pair of grounded electrodes. The electrical current will "channel" along relative conductors in the ground.
SAM EM surveys use a transmit loop and rely on electromagnetic induction to produce secondary fields in buried conductors. 
The transmitter produces a time domain waveform typically in the sub-audio frequency range of 1-20 Hz.
A rapid sampling total field magnetometer acquires both the spatial and induced temporal fields whilst continuously traversing the ground.
The signals are separated by digital filtering. Low pass filtering of the recorded data yields the spatially varying magnetic field. High pass filtering extracts the artificially induced modulation.
Further signal processing extracts parameters of interest.
The main parameters used in Galvanic surveys are: 
- Total magnetic intensity (TMI)
- Total Field MagnetoMetric Resistivity (TFMMR)
- Total Field MagnetoMetric Induced Polarisation (TFMMIP)
The main parameters used in EM surveys are:
- Total Magnetic Intensity (TMI)
- Total Field ElectroMagnetic Induction (TFEMI)
For Galvanic surveys, corrections are applied to the data for
- Influence of the Primary Field (TFMMR)
- Influence of the Normal Field (TFMMR)
- Diurnal variation (TMI only)
- EM Coupling (TFMMR)
- Influence of magnetic inclination and declnation (EQMMR Transform)
Benefits of SAM include:
- Simultaneous acquisition of physically independent data sets.
- Continuous sampling enables cost-effective, high spatial resolution surveys.
- Use of a magnetic sensor allows a “point” measurement as opposed to a volume measurement permitting higher definition than conventional resistivity and IP techniques.
- B-field measurement is superior to dB/dt for late time EM decays.
SAM in action: Sub-Audio Magnetics in Conductive Environments
St Ives Gold Mine, Kambalda WA
- Conventional electrical and electromagnetic surveys are very difficult where regolith is saturated with hypersaline groundwater.
- Resistivity contrast between brine-saturated regolith and fresh bedrock is usually much greater than resistivity contrast within the bedrock.
- SAM has been used at St Ives since 2000.
- SAM maps bedrock faults and shears by detecting their expression as changes in the depth of weathering at the base of the regolith.
- SAM is more effective than EM for this application as the Tx dipole channels current into linear features.
- SAM produces much higher definition data than conventional techniques.
Equivalent MMR
Total Magnetic Intensity